1. Field of the Invention
The present invention concerns a local coil arrangement for magnetic resonance applications of the type having an acquisition coil for acquisition of a magnetic resonance signal excited in an examination subject by means of a transmission coil; and a transponder.
The present invention furthermore concerns an operating method for a magnetic resonance system of the type wherein a temporally static, spatially homogeneous basic magnetic field is generated in an examination region of the magnetic resonance system by means of a basic magnet of the magnetic resonance system, the examination region is charged with a spatially homogeneous radio-frequency transmission signal by means of a transmission antenna of the magnetic resonance system, and a control device of the magnetic resonance system checks whether it receives a transponder signal from a transponder of a local coil arrangement of the type described above.
2. Description of the Prior Art
Local coil arrangements and operating methods of the above general type are known. For example, the transponders are used in order to detect the presence of the local coil arrangement in the examination region of a magnetic resonance system. DE 101 30 617 A1 describes an example of such a system.
Magnetic resonance signals excited in an examination subject (normally a person) are very weak. They can be detected by means of a whole-body coil (which is normally the same as the transmission coil) only with a relatively low SNR. The local coil arrangement therefore is used in order to acquire an excited magnetic resonance signal with better SNR from a spatially limited region.
The examination subject is charged with a relatively strong transmission signal by means of the transmission coil to excite the magnetic resonance signal. A current and/or a voltage are also induced in the acquisition coil of the local coil arrangement. In some cases it can occur that the current and/or the voltage are so high that a risk to the examination subject exists.
In the prior art it is known to provide a fuse to avoid such an endangerment of the examination subject in the AC coil. If too strong a field is induced by the transmission coil, the fuse melts. Although the examination subject is protected by this procedure, the acquisition coil is destroyed. A further disadvantage of the use of fuses is that these negatively influence the SNR.
Furthermore, it is known to use elaborate electronic circuits and conductors that, however, introduce a certain uncertainty factor. It is in particular possible that sheath waves are induced in the conductors.